Polishing kit for magnetic disk

ABSTRACT

A polishing kit for a magnetic disk containing (A) a slurry containing an alumina, (B) an oxidizing agent solution containing an oxidizing agent, and (C) an acid agent solution containing an acid; a polishing kit for a magnetic disk containing (A) a slurry containing an alumina, and (D) an additive solution containing an oxidizing agent and an inorganic acid; and a polishing kit for a magnetic disk containing (A) a slurry containing an alumina, and (C) an acid agent solution containing an acid, wherein the polishing kit is used with an oxidizing agent solution (B) containing an oxidizing agent; and a polishing process for a magnetic disk substrate, including the steps of feeding a liquid mixture containing components of a specified polishing kit to a space between the magnetic disk substrate and a polishing cloth; and polishing the magnetic disk substrate with the liquid mixture. The polishing composition kit can be suitably used for the manufacture of high-quality magnetic disk substrates such as hard disks.

FIELD OF THE INVENTION

The present invention relates to a polishing kit for a magnetic disk, a polishing method for a magnetic disk substrate, and a method for manufacturing a magnetic disk substrate.

BACKGROUND OF THE INVENTION

In order to have a smaller unit recording area and promote higher storage capacity of hard disk drives, a lower flying height of the magnetic head and substantially no surface defects (surface stains) have been desired. In order to lower the flying height of the magnetic head, polishing compositions each containing an alumina, an oxidizing agent and an acid have been studied (Japanese Patent Laid-Open Nos. 2003-147337 and Hei 11-246849).

However, these polishing compositions may not sufficiently exhibit high polishing rates depending upon their storage period after its preparation, thereby giving rise to poor reproducibility. Therefore, in the case where the polishing rate is, for instance, decreased, it is necessary to carry out some operations entailing the extension of the polishing time or maintaining the polishing rate by reducing the dilution fold of the polishing composition, thereby increasing the concentration of the polishing composition upon its use in order to have a sufficient polishing rate. Consequently, the polishing composition has disadvantages such as the composition is more expensive and has lower productivity.

SUMMARY OF THE INVENTION

The present invention relates to:

-   -   [1] a polishing kit for a magnetic disk containing:     -   (A) a slurry containing an alumina;     -   (B) an oxidizing agent solution containing an oxidizing agent;         and     -   (C) an acid agent solution containing an acid;     -   [2] a polishing kit for a magnetic disk containing:     -   (A) a slurry containing an alumina; and     -   (D) an additive solution containing an oxidizing agent and an         inorganic acid;     -   [3] a polishing kit for a magnetic disk containing:     -   (A) a slurry containing an alumina; and     -   (C) an acid agent solution containing an acid,         wherein the polishing kit is used with an oxidizing agent         solution (B) containing an oxidizing agent;     -   [4] a polishing process for a magnetic disk substrate, including         the steps of:     -   feeding a liquid mixture containing (A) a slurry containing an         alumina,     -   (B) an oxidizing agent solution containing an oxidizing agent,         and (C) an acid agent solution containing an acid to a space         between the magnetic disk substrate and a polishing cloth; and     -   polishing the magnetic disk substrate with the liquid mixture;     -   [5] a polishing process for a magnetic disk substrate, including         the steps of:     -   feeding a liquid mixture containing (A) a slurry containing an         alumina, and (D) an additive solution containing an oxidizing         agent and an inorganic acid to a space between the magnetic disk         substrate and a polishing cloth; and     -   polishing the magnetic disk substrate with the liquid mixture.     -   [6] a polishing process for a magnetic disk substrate, including         the steps of:     -   feeding a liquid mixture containing (A) a slurry containing an         alumina, (D) an additive solution containing an oxidizing agent         and an inorganic acid, and (c) an acid agent solution containing         an organic acid to a space between the magnetic disk substrate         and a polishing cloth; and         -   polishing the magnetic disk substrate with the liquid             mixture;     -   [7] a method for manufacturing a polished magnetic disk         substrate including the steps of:     -   (1) mixing (A) a slurry containing an alumina, (B) an oxidizing         agent solution containing an oxidizing agent, and (C) an acid         agent solution containing an acid to give a polishing         composition;     -   (2) pressing the magnetic disk substrate against a polishing         cloth of a polishing platen while applying pressure; and     -   (3) moving the magnetic disk substrate and the polishing platen         while feeding the polishing composition prepared in step (1) to         a space between the magnetic disk substrate and the polishing         cloth, thereby polishing the magnetic disk substrate;     -   [8] a method for manufacturing a polished magnetic disk         substrate including the steps of:     -   (1) mixing (A) a slurry containing an alumina, and (D) an         additive solution containing an oxidizing agent and an inorganic         acid to give a polishing composition;     -   (2) pressing the magnetic disk substrate against a polishing         cloth of a polishing platen while applying pressure; and     -   (3) moving the magnetic disk substrate and the polishing platen         while feeding the polishing composition prepared in step (1) to         a space between the magnetic disk substrate and the polishing         cloth, thereby polishing the magnetic disk substrate; and     -   [9] a method for manufacturing a polished magnetic disk         substrate including the steps of:     -   (1) mixing (A) a slurry containing an alumina, (D) an additive         solution containing an oxidizing agent and an inorganic acid,         and (c) an acid agent solution containing an organic acid to         give a polishing composition;     -   (2) pressing the magnetic disk substrate against a polishing         cloth of a polishing platen while applying pressure; and     -   (3) moving the magnetic disk substrate and the polishing platen         while feeding the polishing composition prepared in step (1) to         a space between the magnetic disk substrate and the polishing         cloth, thereby polishing the magnetic disk substrate.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a polishing kit for a magnetic disk containing an alumina, an oxidizing agent and an acid, which is capable of exhibiting a high polishing rate with excellent reproducibility independent of the length of the storage period; a polishing process for a magnetic disk substrate; and a method for manufacturing a high-quality magnetic disk substrate.

By using the polishing kit for a magnetic disk of the present invention, since a high polishing rate can be exhibited with excellent reproducibility independent of the length of the storage period, an advantage is that such as high-quality magnetic disks can be manufactured at low costs.

These and other advantages of the present invention will be apparent from the following description.

-   -   a) Polishing Composition Kit for Magnetic Disk

The polishing kit for a magnetic disk of the present invention is roughly classified into the following three groups.

(Embodiment a-1) A polishing kit for a magnetic disk containing:

-   -   (A) a slurry containing an alumina;     -   (B) an oxidizing agent solution containing an oxidizing agent;         and     -   (C) an acid agent solution containing an acid.         (Embodiment a-2) A polishing kit for a magnetic disk containing:     -   (A) a slurry containing an alumina; and     -   (D) an additive solution containing an oxidizing agent and an         inorganic acid,         wherein the polishing kit further optionally contains an acid         agent solution (c) containing an organic acid.         (Embodiment a-3) A polishing kit for a magnetic disk containing:     -   (A) a slurry containing an alumina;     -   (C) an acid agent solution containing an acid,         wherein the polishing kit is used with an oxidizing agent         solution (B) containing an oxidizing agent.

One of the great features of the polishing kit for a magnetic disk of the present invention (hereinafter simply referred to as a “kit”) resides in that the kit has the above-mentioned constitution. Since the kit has the above feature, the generation of salts formed by reacting each component and the decomposition of each component can be suppressed, so that the lowering of the polishing rate can be prevented. Therefore, an effect such as a high polishing rate can be shown with excellent reproducibility is exhibited independent of the length of the storage period.

Each component usable in Embodiments a-1 to a-3 are described hereinbelow.

Component (A): Slurry Containing Alumina

The component (A) refers to a component containing at least an alumina, but not substantially containing an organic acid or an oxidizing agent as exemplified later, from the viewpoint of storage stability.

As the alumina usable in the present invention, it is preferable that an aluminum oxide has a purity as alumina of 95% or more, more preferably 97% or more, even more preferably 99% or more, from the viewpoints of reducing the waviness and the surface roughness, increasing the polishing rate, and preventing the surface defects. The α-alumina is preferable, from the viewpoint of increasing the polishing rate, and the intermediate aluminas, such as γ-alumina, δ-alumina, θ-alumina, η-alumina, and κ-alumina are preferable, from the viewpoints of the surface quality and reduction in waviness. In the present invention, the intermediate alumina is a generic term referring to alumina particles other than the α-alumina particles, and concrete examples thereof include γ-alumina, δ-alumina, θ-alumina, η-alumina, κ-alumina, and mixtures thereof. Among the intermediate aluminas, γ-alumina, δ-alumina, θ-alumina, and mixtures thereof are preferable, and from the viewpoint of increasing the polishing rate and reducing the waviness, γ-alumina and θ-alumina are more preferable.

The average primary particle size of the alumina is preferably from 0.005 to 0.8 μm, more preferably from 0.01 to 0.4 μm, from the viewpoint of reducing the waviness. The average secondary particle size of the alumina is preferably from 0.01 to 2 μm, more preferably from 0.05 to 1.0 μm, even more preferably from 0.1 to 0.5 μm, from the viewpoint of reducing the waviness. The average primary particle size of the alumina can be obtained by subjecting the alumina to an image analysis by observing with a scanning electron microscope (preferably from 3000 to 30000 times) or a transmission electron microscope (preferably from 10000 to 300000 times), and determining the particle size. In addition, the average secondary particle size can be determined as a volume-average particle size by using a laser diffraction method.

Among them, when the alumina is an intermediate alumina, the specific surface area determined by the BET method is preferably from 30 to 300 m²/g, more preferably from 50 to 200 m²/g.

As the alumina abrasive, a mixture of the α-alumina and the intermediate alumina is effective, from the viewpoints of increasing the polishing rate and reducing the waviness. In this case, the weight ratio of the α-alumina to the intermediate alumina, α-alumina/intermediate alumina, is preferably from 99/1 to 30/70, more preferably from 97/3 to 40/60, even more preferably from 95/5 to 50/50, and even more preferably from 93/7 to 55/45. Also, as the above-mentioned mixtures, a mixture of the α-alumina and the θ-alumina is preferable.

The content of the alumina is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, even more preferably 1% by weight or more, of the slurry, from the viewpoints of increasing the polishing rate and economic advantages. The content is preferably 60% by weight or less, more preferably 50% by weight or less, 40% by weight or less, of the slurry, from the viewpoint of the dispersion stability of the slurry. Specifically, the content of the alumina is preferably from 0.1 to 60% by weight, more preferably from 0.5 to 50% by weight, even more preferably from 1 to 40% by weight, of the slurry.

In addition, the component (A) may contain an inorganic acid, such as sulfuric acid or nitric acid, an organic acid or salt thereof in the amount necessary for improving the dispersion stability and for preventing caking phenomenon. The content of the inorganic acid or organic acid is preferably from 0.01 to 5% by weight, more preferably from 0.02 to 3% by weight, even more preferably from 0.03 to 1% by weight of the component (A). Also, the content of the salt of the inorganic acid or organic acid is preferably from 0.01 to 30% by weight, more preferably from 0.05 to 20% by weight, even more preferably from 0.1 to 15% by weight of the component (A).

The slurry medium includes water, such as ion-exchanged water, pure water, or ultrapure water, and the medium may also contain a disinfectant, an antibacterial agent, a pH adjustment agent or the like. In addition, the medium may contain an abrasive, such as silica. The amount of water is preferably 40% by weight or more, more preferably from 40 to 99.9% by weight, of the slurry, from the viewpoint of the dispersion stability.

Component (B): Oxidizing Agent Solution Containing Oxidizing Agent

The oxidizing agent solution of the component (B) refers to a solution containing at least an oxidizing agent, but not substantially containing a metal ion, a metal oxide and an organic compound which are causative of the decomposition of the oxidizing agent, from the viewpoint of storage stability. Therefore, the component (B) may contain an organic phosphonic acid, such as hydroxyethylidene-1,1-diphosphonic acid which does not decompose the oxidizing agent.

Here, the content of the metal ion, the metal oxide and the organic compound mentioned above is preferably 2% by weight or less, more preferably 1% by weight or less, of the oxidizing agent solution.

The oxidizing agent usable in the present invention includes a peroxide, a peroxo acid of a metal or a salt thereof, an oxyacid or a salt thereof, a nitrate, a sulfate, a metal salt of an acid, and the like. The oxidizing agent is roughly classified into inorganic oxidizing agents and organic oxidizing agents according to their structures. Concrete examples of those oxidizing agents are as follows. The inorganic oxidizing agent includes hydrogen peroxide; peroxides of alkali metals or alkaline earth metals, such as sodium peroxide, potassium peroxide, calcium peroxide, barium peroxide and magnesium peroxide; peroxocarbonates, such as sodium peroxocarbonate and potassium peroxocarbonate; peroxosulfuric acids or salts thereof, such as ammonium peroxodisulfate, sodium peroxodisulfate, potassium peroxodisulfate and peroxomonosulfuric acid; peroxonitric acids and salts thereof, such as peroxonitric acid, sodium peroxonitrate and potassium peroxonitrate; peroxophosphoric acids or salts thereof, such as sodium peroxophosphate, potassium peroxophosphate and ammonium peroxophosphate; peroxoborates, such as sodium peroxoborate and potassium peroxoborate; peroxochromates, such as potassium peroxochromate and sodium peroxochromate; permanganates, such as potassium permanganate and sodium permanganate; halogeno-acids or derivatives thereof, such as sodium perchlorate, potassium perchlorate, chloric acid, sodium hypochlorite, sodium periodate, potassium periodate, iodic acid and sodium iodate; and metal salts of inorganic acids, such as iron (III) chloride, iron (III) sulfate. The organic oxidizing agent includes percarboxylic acids, such as peracetic acid, performic acid and perbenzoic acid; peroxides, such as t-butyl peroxide and cumene peroxide; and iron salts of organic acids, such as iron (III) citrate. Among them, the inorganic oxidizing agent is preferable, when increase in the polishing rate, availability, and easy handling such as water-solubility are compared. Moreover, in consideration of environmental friendliness, the inorganic peroxide which does not contain a heavy metal is preferable. Furthermore, from the viewpoint of preventing the surface stains on the substrate to be polished, hydrogen peroxide, a peroxosulfate, a halogeno-acid or a derivative thereof is more preferable, and hydrogen peroxide is even more preferable. These oxidizing agents such as peroxides can be used alone or in admixture of two or more kinds.

In addition, the oxidizing agent solution of the component (B) may contain an inorganic acid, such as sulfuric acid, nitric acid, hydrochloric acid or phosphoric acid, as described later.

The content of the oxidizing agent is preferably 0.005% by weight or more, more preferably 0.007% by weight or more, of the oxidizing agent solution, from the viewpoints of increasing the polishing rate and reducing the waviness. Also, the content is preferably 60% by weight or less, more preferably 50% by weight or less, of the oxidizing agent solution, from the viewpoint of the surface quality. Specifically, the content of the oxidizing agent is preferably from 0.005 to 60% by weight, more preferably from 0.007 to 50% by weight, of the oxidizing agent solution.

As a medium of the oxidizing agent solution, water such as ion-exchanged water, pure water or ultrapure water is preferable. The water content is preferably 40% by weight or more, more preferably from 40 to 99.995% by weight of the oxidizing agent solution.

Component (C): Acid Agent Solution Containing Acid

The acid agent solution of the component (C) refers to a solution containing at least an acid, but not substantially containing a metal oxide, such as alumina which would react to the above-mentioned acid. In addition, when the acid agent solution contains an organic acid which is causative of the decomposition of the oxidizing agent, the acid agent solution does not further contain an oxidizing agent. In this case, the content of the oxidizing agent is preferably 2% by weight or less, more preferably 1% by weight or less, of the oxidizing agent solution.

Here, the content of the metal oxide is preferably 2% by weight or less, more preferably 1% by weight or less, of the component (C).

The acid includes an inorganic acid and an organic acid.

The inorganic acid includes nitrogen-containing inorganic acids, such as nitric acid and nitrous acid; sulfur-containing inorganic acids, such as sulfuric acid, sulfurous acid and amide sulfuric acid; phosphor-containing inorganic acids, such as phosphoric acid, pyrophosphoric acid, polyphosphoric acid and phosphonic acid; halogen-containing inorganic acids, such as hydrochloric acid and bromic acid; and the like. Among them, nitric acid, nitrous acid, sulfuric acid, sulfurous acid and amide sulfuric acid are preferable, more preferably sulfuric acid, sulfurous acid and amide sulfuric acid, even more preferably sulfuric acid, from the viewpoint of increasing the polishing rate. Also, the content of the inorganic acid is preferably 0.005% by weight or more, more preferably 0.007% by weight or more, of the acid agent solution. The content is preferably 60% by weight or less, more preferably 50% by weight or less, of the acid agent solution, from the viewpoints of the surface quality. Specifically, the content of the inorganic acid is preferably from 0.005 to 60% by weight, more preferably from 0.007 to 50% by weight, of the acid agent solution.

The organic acid preferably has a pK1 of 7 or less, more preferably 5 or less, even more preferably 4 or less, even more preferably 2 or less, from the viewpoints of increasing the polishing rate and reducing the waviness. Here, the pK1 refers to a logarithmic value of an inverse of a first acid dissociation constant at 25° C. The pK1 of each compound is listed in, Kagaku Binran (Kiso-hen) II, Fourth Revision, pp. 316-325 (Edit. by Nippon Kagakukai), and the like.

As the organic acid, sulfur-containing organic acids, carboxylic acids and phosphor-containing organic acids are preferable, from the viewpoints of increasing the polishing rate, reducing the waviness and preventing the surface stains. Concrete examples thereof are as follows. The organic acid includes monocarboxylic acids, such as formic acid, acetic acid, glycolic acid, lactic acid, propanoic acid, hydroxypropanoic acid, butyric acid, benzoic acid, and glycine; polycarboxylic acids, such as oxalic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, itaconic acid, malic acid, tartaric acid, citric acid, isocitric acid, phthalic acid, nitrilotriacetic acid and ethylenediaminetetraacetic acid; sulfur-containing organic acid, such as methanesulfonic acid, paratoluenesulfonic acid and alkylsulfuric acid; and phosphor-containing organic acid, such as ethylphosphoric acid, butylphosphoric acid, laurylphosphoric acid, phosphonohydroxyacetic acid, hydroxyethylidene-1,1-diphosphonic acid, phosphonobutane tricarboxylic acid and ethylenediaminetetramethylene phosphonic acid. Among them, the sulfur-containing organic acids or the phosphor-containing organic acids are preferable, more preferably organic sulfonic acids or organic phosphonic acids, even more preferably organic sulfonic acids, from the viewpoints of increasing the polishing rate and reducing the waviness. In addition, the sulfur-containing organic acids and carboxylic acids are preferable, more preferably organic sulfonic acids and polycarboxylic acids, from the viewpoints of preventing the surface stains of the object to be polished. These compounds can be used alone or in admixture.

The content of the organic acid is preferably 0.005% by weight or more, more preferably 0.007% by weight or more, of the acid agent solution, from the viewpoints of increasing the polishing rate and reducing the waviness. Also, the content is preferably 60% by weight or less, more preferably 50% by weight or less, of the acid agent solution, from the viewpoints of the surface quality and economic advantages. Specifically, the content of the organic acid is preferably from 0.005 to 60% by weight, more preferably from 0.007 to 50% by weight, of the above-mentioned acid agent solution.

As a medium of the acid agent solution, water such as ion-exchanged water, pure water or ultrapure water is preferable. The water content is preferably 40% by weight or more, more preferably from 40 to 99.95% by weight, of the acid agent solution.

The pH of the acid agent solution is preferably 6 or less, more preferably from 0.1 to 5, even more preferably from 0.2 to 4. The pH can be adjusted by adding a basic substance, such as an aqueous ammonia, sodium hydroxide, potassium hydroxide, or a salt such as an ammonium salt, a sodium salt, or a potassium salt of the contained acid.

Component (D): Additive Solution Containing Oxidizing Agent and Inorganic Acid

The additive solution of the component (D) refers to a solution containing at least the oxidizing agent and the inorganic acid mentioned above, but not substantially containing a metal ion, a metal oxide and an organic compound which are causative of the decomposition of the oxidizing agent. Specifically, the additive solution may contain an organic phosphonic acid, such as hydroxyethylidene-1,1-diphosphonic acid which does not decompose the oxidizing agent. The content of the oxidizing agent and the content of the inorganic acid are the same as those mentioned above.

The total amount of these components is preferably 0.01% by weight or more, more preferably from 0.01 to 80% by weight, even more preferably from 0.03 to 60% by weight, even more preferably from 0.05 to 50% by weight, of the additive solution.

A preferred combination of the oxidizing agent and the inorganic acid usable in the component (D) includes a combination of hydrogen peroxide and sulfuric acid.

The content of the metal ion, the metal oxide and the organic compound is preferably 2% by weight or less, more preferably 1% by weight or less, of the component (D).

As a medium of the additive solution, water such as ion-exchanged water, pure water or ultrapure water is preferable. The water content is preferably 20% by weight or more, more preferably from 20 to 99.99% by weight, of the additive solution.

Component (c): Acid Agent Solution Containing Organic Acid

The component (c) refers to an acid agent solution containing at least an organic acid, and also being used together with the component (D). The kind and the amount of the organic acid are not particularly limited, as long as they are the same as those mentioned in the component (C).

Each kit of Embodiments a-1, a-2 and a-3 is used by formulating each component, so that the content of each of the alumina, the oxidizing agent, and the acid of the polishing composition containing the constituents of each kit is within a specified range. In addition, there can be used in admixture of water, such as ion-exchanged water, pure water or ultrapure water, as occasion demands.

The content of the alumina is preferably 0.05% by weight or more, more preferably 0.1% by weight or more, even more preferably 0.5% by weight or more, even more preferably 1% by weight or more, of the polishing composition, from the viewpoints of increasing the polishing rate and reducing the waviness. Also, the content is preferably 40% by weight or less, more preferably 30% by weight or less, even more preferably 25% by weight or less, even more preferably 20% by weight or less, of the polishing composition, from the viewpoints of the surface quality and economic advantages. Specifically, the content of the alumina is preferably from 0.05 to 40% by weight, more preferably from 0.1 to 30% by weight, even more preferably from 0.5 to 25% by weight, even more preferably from 1 to 20% by weight, of the polishing composition.

The content of the oxidizing agent is preferably 0.002% by weight or more, more preferably 0.005% by weight or more, even more preferably 0.007% by weight or more, even more preferably 0.01% by weight or more, of the polishing composition, from the viewpoints of increasing the polishing rate, reducing the waviness and reducing stains on the substrate. Also, the content is preferably 20% by weight or less, more preferably 15% by weight or less, even more preferably 10% by weight or less, even more preferably 5% by weight or less, of the polishing composition, from the viewpoints of the surface quality and economic advantages. Specifically, the content of the oxidizing agent is preferably from 0.002 to 20% by weight, more preferably from 0.005 to 15% by weight, even more preferably from 0.007 to 10% by weight, even more preferably from 0.01 to 5% by weight, of the polishing composition.

The content of the acid is preferably 0.002% by weight or more, more preferably 0.005% by weight or more, even more preferably 0.007% by weight or more, even more preferably 0.01% by weight or more, of the polishing composition, in order to satisfy the increase in the polishing rate, the reduction in the waviness and the reduction in stains on the substrate. Also, the content is preferably 20% by weight or less, more preferably 15% by weight or less, even more preferably 10% by weight or less, even more preferably 5% by weight or less, of the polishing composition, from the viewpoints of the surface quality and economic advantages. Specifically, the content of the acid is preferably from 0.002 to 20% by weight, more preferably from 0.005 to 15% by weight, even more preferably from 0.007 to 10% by weight, even more preferably from 0.01 to 5% by weight, of the polishing composition.

In addition, an inorganic salt, a thickener, an anticorrosive agent, a basic substance and the like can be added to each component of the kit of the present invention, as occasion demands. These compounds can be used alone or in admixture of two or more kinds. The content thereof is preferably from 0.05 to 20% by weight, more preferably from 0.05 to 10% by weight, even more preferably from 0.05 to 5% by weight, of the polishing composition obtainable from the kit, from the viewpoint of economic advantages.

Furthermore, there can be added a disinfectant or an antibacterial agent, to each component of the kit, as occasion demands. The content of the disinfectant and the antibacterial agent is preferably from 0.0001 to 0.1% by weight, more preferably from 0.001 to 0.05% by weight, even more preferably from 0.002 to 0.02% by weight, of the polishing composition obtainable from the kit, from the viewpoint of exhibiting its function and from the viewpoints of the influence on polishing performance and economic advantages.

The balance of the polishing composition is water. The water content is preferably from 55 to 99% by weight, more preferably from 60 to 99% by weight, even more preferably from 70 to 95% by weight, of the polishing composition.

The kit of the present invention has an advantage of being able to have highly excellent storage stability by separately storing each of the components such as the component (A), without mixing the other components with each other. Specific embodiments of the kit include a kit housed in a vessel, such as a can, a drum or other container, which is made of a material having a property of being resistant to each of the components such as the component (A).

Each component of the kit can be prepared by adding and mixing the desired components by a given method.

It is preferable that the pH of the polishing composition obtained by combining the components of the kit of the present invention is appropriately determined, depending upon the kinds of the object to be polished and the required properties. The lower the pH, the more preferable, from the viewpoints of increasing the polishing rate and reducing the waviness, and the closer the pH to 7, the more preferable, from the viewpoints of prevention of the corrosion of the processing machine and safety for the operator. Accordingly, considering both viewpoints, the pH is preferably 0.1 or more and less than 6, more preferably 0.5 or more and less than 5, even more preferably 1 or more and less than 4, even more preferably 1 or more and less than 3. The pH of the kit can be adjusted by properly adding an inorganic acid, such as nitric acid or sulfuric acid; an organic acid, such as a hydroxycarboxylic acid, a polycarboxylic acid, an aminopolycarboxylic acid or an amino acid, a metal salt or an ammonium salt thereof; or a basic substance, such as, an aqueous ammonia, sodium hydroxide, potassium hydroxide or an amine, in a desired amount.

The magnetic disk substrate, which is the substrate to be polished as a subject for the present invention, is used as a substrate for a magnetic recording medium. Concrete examples of the magnetic disk substrate include representatively a substrate made of an aluminum alloy plated with Ni—P alloy, and there are also included a substrate made of glass or glassy carbon, instead of the aluminum alloy, and plated with Ni—P thereon; or a substrate coated with various metallic compounds by plating or deposition, instead of the substrate plated with Ni—P.

The kit of the present invention is especially effective in the polishing step, and the kit can be similarly applied to other steps, for instance, in the lapping step, and the like.

-   -   b) Polishing Process for Magnetic Disk Substrate

The polishing process for a magnetic disk substrate of the present invention is roughly classified into the following embodiments: (Embodiment b-1) a polishing process for a magnetic disk substrate including the steps of:

-   -   feeding a liquid mixture containing (A) a slurry containing an         alumina, (B) an oxidizing agent solution containing an oxidizing         agent, and (C) an acid agent solution containing an acid to a         space between the magnetic disk substrate and a polishing cloth;         and     -   polishing the magnetic disk substrate with the liquid mixture;         (Embodiment b-2) a polishing process for a magnetic disk         substrate including the steps of:     -   feeding a liquid mixture containing (A) a slurry containing an         alumina, and (D) an additive solution containing an oxidizing         agent and an inorganic acid to a space between the magnetic disk         substrate and a polishing cloth; and     -   polishing the magnetic disk substrate with the liquid mixture;         and         (Embodiment b-3) a polishing process for a magnetic disk         substrate including the steps of:     -   feeding a liquid mixture containing (A) a slurry containing an         alumina, (D) an additive solution containing the oxidizing agent         and inorganic acid and (c) an acid agent solution containing an         organic acid to a space between the magnetic disk substrate and         a polishing cloth; and     -   polishing the magnetic disk substrate with the liquid mixture.

The components (A), (B), (C), (D) and (c) and the magnetic disk substrate, and the like usable in the polishing process for a magnetic disk substrate of the present invention may be the same as any of those mentioned above. Therefore, the liquid mixture usable in the above-mentioned Embodiment b-1 is the same as the polishing composition obtained by formulating the constituents of the kit of Embodiment a-1, and the liquid mixture usable in Embodiment b-2 or b-3 is the same as the polishing composition obtained by formulating the constituents of the kit of Embodiment a-2.

Also, the polishing cloth is not particularly limited as long as the polishing cloth is used in a general polishing process for a magnetic disk substrate. The polishing cloth made of a porous organic polymer is preferable.

In the polishing process according to the above-mentioned Embodiments b-1 to b-3, for instance, the magnetic disk substrate can be polished by clamping a magnetic disk substrate with polishing platens to which a polishing cloth made of a porous organic polymer and the like is attached; feeding the above-mentioned liquid mixture to a surface to be polished; and moving the polishing platens and the substrate, while applying pressure. The polishing platen is not particularly limited as long as the polishing platen is used in the general polishing process for a magnetic disk substrate. Also, other conditions such as the kind of polishing machine, polishing temperature, rotational speed and feed amount of the polishing composition are not particularly limited.

An example of the polishing process for Embodiments b-1 to b-3 is preferably a process including the step of feeding a liquid mixture obtained by charging each component mentioned above into a vessel while stirring before polishing. The term “before polishing” as referred to herein means a stage before the polishing is carried out. The time period up to a point of polishing after mixing is preferably shorter, from the viewpoint of stability of the liquid mixture. The structure, the size and the material of the vessel are not particularly limited, and may be properly determined according to the feed amount of the liquid mixture and the like.

Another example of the polishing process for Embodiments b-1 to b-3 is a process including the steps of connecting a feeding means for feeding each component in the same part or in a different part in the feeding of each component; and feeding a liquid mixture with the feeding means in which each component is allowed to merge to each other. As the feeding means, a pipe is preferably used.

For instance, the polishing process for Embodiment b-1 includes a process including the steps of feeding the component (A), the component (B) and the component (C) into each of a first pipe, a second pipe and a third pipe; mixing the above-mentioned components (A) to (C) in a fourth pipe which is connected to the first pipe, the second pipe and the third pipe; and thereafter feeding the resulting liquid mixture from the fourth pipe. Furthermore, in order to mix water therewith, a fifth pipe may be connected to one or more of the first to the fourth pipes. The connecting point, the size, the shape, and the arrangement of each of the first to the third pipes on the fourth pipe are not generally limited because they differ depending upon the number and the size of the magnetic disk substrate to be polished per each time, the concentration of a compound, such as the alumina, the oxidizing agent, or the acid contained in each component.

Similarly, the polishing process of Embodiment b-2 includes a process including the steps of feeding the components (A) and (D) into each of a first pipe and a second pipe; mixing the components (A) and (D) in a third pipe connected to the first pipe and the second pipe; and thereafter feeding the resulting liquid mixture from the third pipe. Furthermore, in order to mix water therewith, a fourth pipe may be connected to one or more of the first to the third pipes. The polishing process of Embodiment b-3 includes a process including the steps of feeding the component (A), the component (D) and the component (c) into each of a first pipe, a second pipe and a third pipe; mixing the components (A), (D) and (c) in a fourth pipe connected to the first pipe, the second pipe and the third pipe; and thereafter feeding the resulting liquid mixture from the fourth pipe. Furthermore, in order to mix water therewith, a fifth pipe may be connected to one or more of the first to the fourth pipes. In the third pipe of Embodiment b-2 and the fourth pipe of Embodiment b-3, the connecting point to the other pipes, the size, the shape, the arrangement of each of the first to the fourth pipes are not generally limited, because they differ depending upon the number and the size of a magnetic disk substrate to be polished per each time, the concentration of a compound, such as the alumina, the oxidizing agent, and the acid contained in each component.

By using the polishing process for a magnetic disk substrate of the present invention having the above constitution, an effect that a high polishing rate can be shown with excellent reproducibility without being dependent upon the storage period is exhibited.

-   -   c) Method for Manufacturing Magnetic Disk Substrate

The method for manufacturing a magnetic disk substrate of the present invention is roughly classified into the following embodiments: (Embodiment c-1) a method for manufacturing a magnetic disk substrate including the following steps of:

-   -   (1) mixing (A) a slurry containing an alumina, (B) an oxidizing         agent solution containing an oxidizing agent, and (C) an acid         agent solution containing an acid to give a polishing         composition;     -   (2) pressing the magnetic disk substrate against a polishing         cloth of a polishing platen while applying pressure; and     -   (3) moving the magnetic disk substrate and the polishing platen         while feeding the polishing composition prepared in step (1) to         a space between the magnetic disk substrate and the polishing         cloth, thereby polishing the magnetic disk substrate;         (Embodiment c-2) a method for manufacturing a magnetic disk         substrate including the following steps of:     -   (1) mixing (A) a slurry containing an alumina, and (D) an         additive solution containing an oxidizing agent and an inorganic         acid to give a polishing composition;     -   (2) pressing the magnetic disk substrate against a polishing         cloth of a polishing platen while applying pressure; and     -   (3) moving the magnetic disk substrate and the polishing platen         while feeding the polishing composition prepared in step (1) to         a space between the magnetic disk substrate and the polishing         cloth, thereby polishing the magnetic disk substrate; and         (Embodiment c-3) a method for manufacturing a magnetic disk         substrate including the following steps of:     -   (1) mixing (A) a slurry containing an alumina, (D) an additive         solution containing an oxidizing agent and an inorganic acid,         and (c) an acid solution containing an organic acid to give a         polishing composition:     -   (2) pressing the magnetic disk substrate against a polishing         cloth of a polishing platen while applying pressure; and     -   (3) moving the magnetic disk substrate and the polishing platen         while feeding the polishing composition prepared in step (1) to         a space between the magnetic disk substrate and the polishing         cloth, thereby polishing the magnetic disk substrate.

The above-mentioned components (A), (B), (C), (D) and (c), the magnetic disk substrate, the polishing cloth and polishing platen and the like may be the same as any of those mentioned above. Therefore, the polishing composition usable in the above-mentioned Embodiment c-1 is the same as the polishing composition obtained by formulating the constituents of the kit of Embodiment a-1, and the polishing composition usable in Embodiments c-2 and c-3 is the same as the polishing composition obtained by formulating the constituents of the kit of Embodiment a-2.

In the above-mentioned polishing process, the pressure applied by pressing is preferably from 1 to 20 kPa, more preferably from 3 to 15 kPa, from the viewpoints of increasing the surface smoothness, reducing the surface defects and increasing the polishing rate.

The method of moving a substrate and a polishing platen is not particularly limited, as long as the method is known.

By using the method for manufacturing a magnetic disk substrate of the present invention having the above constitution, there are some advantages such as a high-quality magnetic disk substrate in which surface smoothness is increased and surface defects are reduced can be manufactured economically advantageously with excellent reproducibility.

In the method for manufacturing a magnetic disk substrate according to Embodiments c-1 to c-3, it is preferable to feed the liquid mixture obtained by charging each component mentioned above into a vessel while stirring before polishing. The term “before polishing” as referred to herein means a stage before the polishing is carried out, and the time period up to a point of polishing after mixing is preferably shorter, from the viewpoint of stability of the liquid mixture. The structure, the size and the material of the vessel are not particularly limited, and may be properly determined according to the feed amount of the liquid mixture and the like.

Another example includes a method including the steps of connecting a feeding means for feeding each component in the same part or in the different part in the feeding of each component; and feeding a liquid mixture with the feeding means in which each component is allowed to merge to each other. As the feeding means, a pipe is preferably used.

EXAMPLES

The following examples further describe and demonstrate embodiments of the present invention. The examples are given solely for the purposes of illustration and are not to be construed as limitations of the present invention.

Examples 1 to 3, Comparative Examples 1 to 4

[Preparation of Polishing Composition]

A 2-L polyethylene resin vessel was charged with 12.75% by weight of α-alumina (average primary particle size: 0.07 μm, average secondary particle size: 0.3 μm, specific surface area: 15 m²/g, purity: 99.9%), 0.8% by weight of sulfuric acid, 4.28% by weight of citric acid, 7.31% by weight of a 35% aqueous hydrogen peroxide (2.56% by weight as hydrogen peroxide), and balance ion-exchanged water, while stirring, so as to have a total weight of 1.5 kg, to give a polishing composition. Further, a 4-L polyethylene resin vessel was charged with this polishing composition and ion-exchanged water in a formulation ratio (weight ratio) of 1:4 so as to have a total weight of 4 kg, while stirring, to give a polishing composition of Reference Example 1.

A 2-L polyethylene resin vessel was charged with each of a component (A), a component (B) or (D), and component (C) or (c) of the polishing composition kit of Examples 1 to 3 and Comparative Examples 1 to 4 having the components shown in Table 1, and tightly sealed, and the components were allowed to stand at 60° C. for 28 days. After allowing the components to stand, a 4-L polyethylene resin vessel was charged with the components of each polishing composition kit and ion-exchanged water in a formulation ratio (weight ratio) shown in Table 1 so as to have a total weight of 4 kg, while stirring, to give a polishing composition of Examples 1 to 3 and Comparative Examples 1 to 4.

Here, as the component (A), a slurry containing 12.75% by weight of α-alumina in which water was used as a medium was used. In the table, those listed with other components mean that these components were contained in the above slurry in given amounts.

As to the component (B), 7.31% by weight of a 35% aqueous hydrogen peroxide (2.56% by weight as hydrogen peroxide) was used. In the table, those listed with other components mean that these components were contained in the aqueous hydrogen peroxide in given amounts.

As to the component (C), sulfuric acid and citric acid were used. The content was the amount listed in the table. As the component (c), citric acid was used. The content was the amount listed in the table. As the component (D), sulfuric acid and an aqueous hydrogen peroxide were used. The content was the amount listed in the table.

Each of the resulting polishing compositions was evaluated for its polishing property, and the polishing rate was determined. A relative value (relative polishing rate) of each polishing composition of each Example or Comparative Example was calculated based on the polishing rate of the polishing composition in Reference Example 1 as a standard value 1. The results are shown in Table 1. Here, the determinations of the polishing process and the polishing rate are as follows.

[Polishing Process]

A substrate surface made of a Ni—P plated aluminum alloy, the substrate surface having an average surface roughness Ra of 0.2 μm, as determined by Talystep commercially available from Rank Taylor-Hobson Limited (size of tip end of profilometer: 25 μm×25 μm, by-pass filter: 80 μm, measurement length: 0.64 mm), a thickness of 1.27 mm and a diameter of 3.5 inches (diameter of 95.0 mm) was polished with a double-sided processing machine under set conditions given below, to give a polished Ni—P plated, aluminum alloy substrate usable for a substrate for magnetic recording media.

Set conditions are as follows.

<Set Conditions for Double-Sided Processing Machine>

-   Double-sided processing machine: double-sided processing machine,     Model 9B, manufactured by SPEEDFAM CO., LTD. -   Processing pressure: 9.8 kPa -   Polishing Pad: “H9900S” (manufactured by FUJIBO Co., Ltd.). -   Rotational speed of platen: 50 r/min -   Feeding flow amount for a polishing composition: 100 ml/min -   Polishing time period: 5 minutes -   Number of substrates introduced: 10     [Polishing Rate]

Weights of each substrate before and after polishing were measured using a device commercially available from Sartorius under the trade name of “BP-210S.” Change in weight of each substrate was obtained, and an average of 10 substrates was defined as an amount reduced, and a value obtained by dividing the amount reduced by the polishing time was referred to as a rate of weight reduced. The rate of weight reduced was introduced into the following equation and converted to a polishing rate (μm/min.). Rate of Weight Reduced (g/min.)={Weight Before Polishing (g)−Weight After Polishing (g)}/Polishing Time (min.) Polishing Rate (μm/min.)=Rate of Weight Reduced (g/min.)/Area of One Side of Substrate (mm²)/Ni—P Plating Density (g/cm³)×10⁶ TABLE 1 Formulation Ratio Relative Components of Polishing Composition Kit (Weight Ratio) Polishing Ex. No. i ii iii i/ii/iii/ion-exchanged water pH Rate Ex. 1 α-Alumina (12.75) A H₂O₂ (2.56) B Sulfuric Acid (0.8) C 1:1:1:2 1.5 1.0 Citric Acid (4.28) Ex. 2 α-Alumina (12.75) A H₂O₂ (2.56) D Citric Acid (4.28) c 1:1:1:2 1.5 1.0 Sulfuric Acid (0.8) Ex. 3 α-Alumina (12.75) A H₂O₂ (2.56) B Sulfuric Acid (0.7) C 1:1:1:2 1.5 1.0 Sulfuric Acid (0.1) Citric Acid (4.28) Ref. α-Alumina (12.75) — (After the preparation, polishing evaluation was 1:—:—:4 1.5 1.0 Ex. 1 H₂O₂ (2.56) immediately carried Out at 60° C. without storing.) Sulfuric Acid (0.8) Citric Acid (4.28) Comp. α-Alumina (12.75) — — — Sulfuric Acid (0.8) C 1:—:1:3 1.5 0.78 Ex. 1 H₂O₂ (2.56) Citric Acid (4.28) Comp. α-Alumina (12.75) A H₂O₂ (2.56) — — 1:1:—:3 1.7 0.89 Ex. 2 Sulfuric Acid (0.8) Citric Acid (4.28) Comp. α-Alumina (12.75) — H₂O₂ (2.56) B — — 1:1:—:3 2.8 0.89 Ex. 3 Sulfuric Acid (0.8) Citric Acid (4.28) Comp. α-Alumina (12.75) — — — — — 1:—:—:4 2.8 0.56 Ex. 4 H₂O₂ (2.56) Sulfuric Acid (0.8) Citric Acid (4.28) Inside the parenthesis ( ) shows formulation amounts (% by weight), and balance is water.

As shown in the results of Table 1, it can be seen that the polishing rate after the storage at 60° C. of each of the polishing compositions obtained from the polishing composition kit of Examples 1 to 3 is maintained at a high level with excellent reproducibility as compared to the case of the polishing rate of Reference Example 1. By contrast, the polishing rate after the storage at 60° C. of each of the polishing compositions obtained from the polishing composition kit of Comparative Examples 1 to 4 is dramatically decreased as compared to the polishing rate of the case where the polishing composition was evaluated for the polishing property immediately after the preparation without storage (Reference Example 1).

Examples 4 and 5 and Comparative Examples 5 to 7

The same procedures as in Example 1 were carried out except that each of the polishing composition kits of Examples 4 and 5 and Comparative Examples 5 to 7 having the components shown in Table 2 was used, to give a polishing composition. The resulting polishing composition was evaluated for its polishing property. A relative value of the polishing rate of each polishing composition of each Example or Comparative Example was calculated based on the polishing rate of the polishing composition in Reference Example 2 as a standard value 1. The results are shown in Table 2. Here, the polishing composition of Reference Example 2 was prepared in the same manner as in the polishing composition of Reference Example 1 except that the components as shown in Table 2 were used. TABLE 2 Formulation Ratio Relative Components of Polishing Composition Kit (Weight Ratio) Polishing Ex. No. i ii iii i/ii/iii/ion-exchanged water pH Rate Ex. 4 α-Alumina (12.75) A H₂O₂ (2.56) B Sulfuric Acid (7.4) C 1:1:1:2 1.0 1.0 Ex. 5 α-Alumina (12.75) A H₂O₂ (2.56) D — — 1:1:—:3 1.0 1.0 Sulfuric Acid (7.4) Ref. α-Alumina (12.75) — (After the preparation, polishing evaluation was 1:—:—:4 1.0 1.0 Ex. 2 H₂O₂ (2.56) immediately carried out at 60° C. without storing.) Sulfuric Acid (7.4) Comp. α-Alumina (12.75) — — — Sulfuric Acid (7.4) C 1:—:1:3 1.0 0.75 Ex. 5 H₂O₂ (2.56) Comp. α-Alumina (12.75) — H₂O₂ (2.56) B — — 1:1:—:3 2.3 0.88 Ex. 6 Sulfuric Acid (7.4) Comp. α-Alumina (12.75) — — — — — 1:—:—:3 2.3 0.25 Ex. 7 H₂O₂ (2.56) Sulfuric Acid (7.4) Inside the parenthesis ( ) shows formulation amounts (% by weight), and balance is water.

As shown in the results of Table 2, it can be seen that the polishing rate after the storage at 60° C. of each of the polishing compositions obtained from the polishing composition kit of Examples 4 and 5 is maintained at a high level with excellent reproducibility as compared to the case of the polishing rate of Reference Example 2. By contrast, the polishing rate after the storage at 60° C. of each of the polishing compositions obtained from the polishing composition kit of Comparative Examples 5 to 7 is dramatically decreased as compared to the polishing rate of the case where the polishing composition was evaluated for the polishing property immediately after the preparation without storage (Reference Example 2).

Example 6 and Comparative Examples 8 to 11

The same procedures as in Example 1 were carried out except that each of the polishing composition kits of Example 6 and Comparative Examples 8 to 11 having the components shown in Table 3 was used, to give a polishing composition. The resulting polishing composition was evaluated for its polishing property. A relative value of the polishing rate of each polishing composition of each Example or Comparative Example was calculated based on the polishing rate of the polishing composition in Reference Example 3 as a standard value 1. The results are shown in Table 3. Here, the polishing composition of Reference Example 3 was prepared in the same manner as in Reference Example 1 except to have the components as shown in Table 3. TABLE 3 Formulation Ratio Relative Components of Polishing Composition Kit (Weight Ratio) Polishing Ex. No. i ii iii i/ii/iii/ion-exchanged water pH Rate Ex. 6 α-Alumina (12.75) A H₂O₂ (2.56) B Citric Acid (14.5) C 1:1:1:2 1.8 1.0 Ref. α-Alumina (12.75) — (After the preparation, polishing 1:—:—:4 1.8 1.0 Ex. 3 H₂O₂ (2.56) evaluation was immediately carried out at Citric Acid (14.5) 60° C. without storing.) Comp. α-Alumina (12.75) A H₂O₂ (2.56) — — — 1:1:—:3 2.0 0.75 Ex. 8 Citric Acid (14.5) Comp. α-Alumina (12.75) — — — Citric Acid (14.5) C 1:—:1:3 1.8 0.63 Ex. 9 H₂O₂ (2.56) Comp. α-Alumina (12.75) — H₂O₂ (2.56) B — — 1:1:—:3 2.8 0.75 Ex. 10 Citric Acid (14.5) Comp. α-Alumina (12.75) — — — — — 1:—:—:4 2.8 0.50 Ex. 11 H₂O₂ (2.56) Citric Acid (14.5) Inside the parenthesis ( ) shows formulation amounts (% by weight), and balance is water. θ-Alumina: secondary average particle size: 0.2 μm, specific surface area: 120 m²/g, purity: 99.9%

As shown in the results of Table 3, it can be seen that the polishing rate after the storage at 60° C. of the polishing composition obtained from the polishing composition kit of Example 6 is maintained at a high level with excellent reproducibility as compared to the case of the polishing rate of Reference Example 3. By contrast, the polishing rate after the storage at 60° C. of each of the polishing compositions obtained from the polishing composition kit of Comparative Examples 8 to 11 is dramatically decreased as compared to the polishing rate of the case where the polishing composition was evaluated for the polishing property immediately after the preparation without storage (Reference Example 3).

Examples 7 to 18 and Comparative Examples 12 to 18

The same procedures as in Example 1 were carried out except that each of the polishing composition kits of Examples 7 to 18 and Comparative Examples 12 to 18 having the components shown in Tables 4 and 5 was used, to give a polishing composition. The resulting polishing composition was evaluated for its polishing property. A relative value of the polishing rate of each polishing composition of each Example or Comparative Example was calculated based on the polishing rate of the polishing composition in Reference Example 4 as a standard value 1. The results are shown in Tables 4 and 5. Here, the polishing composition of Reference Example 4 was prepared in the same manner as in Reference Example 1 except to have the components as shown in Tables 4 and 5. TABLE 4 Formulation Ratio (Weight Ratio) Relative Components of Polishing Composition Kit i/ii/iii/ion-exchanged Polishing Ex. No. i ii iii water pH Rate Ex. 7 α-Alumina (12.75) A H₂O₂ (2.56) B Sulfuric Acid (0.8) C 1:1:1:2 2.0 1.0 θ-Alumina (2.56) Citric Acid (4.28) Ammonium Sulfate (9.35) Ex. 8 α-Alumina (12.75) A H₂O₂ (2.56) B Sulfuric Acid (0.7) C 1:1:1:2 2.1 1.0 θ-Alumina (2.56) Citric Acid (4.28) Sulfuric Acid (0.1) Ammonium Sulfate (9.35) Ex. 9 α-Alumina (12.75) A H₂O₂ (2.56) B Sulfuric Acid (0.8) C 1:1:1:2 2.0 1.0 θ-Alumina (2.56) Citric Acid (4.28) Ammonium Sulfate (9.35) Ex. 10 α-Alumina (12.75) A H₂O₂ (2.56) B Sulfuric Acid (0.8) C 1:1:1:2 2.0 1.0 θ-Alumina (2.56) Ammonium Sulfate (9.35) Citric Acid (4.28) Ex. 11 α-Alumina (12.75) A H₂O₂ (2.56) D Citric Acid (4.28) c 1:1:1:2 2.0 1.0 θ-Alumina (2.56) Sulfuric Acid (0.8) Ammonium Sulfate (9.35) Ex. 12 α-Alumina (12.75) A H₂O₂ (2.56) D Citric Acid (4.28) c 1:1:1:2 2.1 1.0 θ-Alumina (2.56) Sulfuric Acid (0.7) Sulfuric Acid (0.1) Ammonium Sulfate (9.35) Ex. 13 α-Alumina (12.75) A H₂O₂ (2.56) D Citric Acid (4.28) c 1:1:1:2 2.0 1.0 θ-Alumina (2.56) Sulfuric Acid (0.8) Ammonium Sulfate (9.35) Ex. 14 α-Alumina (12.75) A H₂O₂ (2.56) D Citric Acid (4.28) c 1:1:1:2 2.0 1.0 θ-Alumina (2.56) Sulfuric Acid (0.8) Ammonium Sulfate (9.35) Ex. 15 α-Alumina (12.75) A H₂O₂ (2.56) B Sulfuric Acid (0.7) C 1:1:1:2 2.0 1.0 θ-Alumina (2.56) Sulfuric Acid (0.1) Citric Acid (4.28) Ammonium Sulfate (9.35) Ex. 16 α-Alumina (12.75) A H₂O₂ (2.56) B Sulfuric Acid (0.6) C 1:1:1:2 2.0 1.0 θ-Alumina (2.56) Sulfuric Acid (0.2) Citric Acid (4.28) Ammonium Sulfate (9.35) Ex. 17 α-Alumina (12.75) A H₂O₂ (2.56) D Sulfuric Acid (0.1) c 1:1:1:2 2.0 1.0 θ-Alumina (2.56) Sulfuric Acid (0.7) Citric Acid (4.28) Ammonium Sulfate (9.35) Ex. 18 α-Alumina (12.75) A H₂O₂ (2.56) B Sulfuric Acid (0.7) C 1:1:1:2 2.1 1.0 θ-Alumina (2.56) Citric Acid (4.28) Ammonium Sulfate (7.0) Ammonium Sulfate (2.35) Sulfuric Acid (0.1) Ref. α-Alumina (12.75) — (After the preparation, polishing evaluation was immediately 1:—:—:4 2.0 1.0 Ex. 3 θ-Alumina (2.56) carried out at 60° C. without storing.) H₂O₂ (2.56) Sulfuric Acid (0.8) Citric Acid (4.28) Ammonium Sulfate (9.35) Inside the parenthesis ( ) shows formulation amounts (% by weight), and balance is water.

TABLE 5 Formulation Ratio Relative Components of Polishing Composition Kit (Weight Ratio) Polishing Ex. No. i ii i/ii/ion-exchanged water pH Rate Ref. α-Alumina (12.75) — (After the preparation, 1:—:4 2.0 1.0 Ex. 4 θ-Alumina (2.56) polishing evaluation was H₂O₂ (2.56) immediately carried out at Sulfuric Acid (0.8) 60° C. without storing.) Citric Acid (4.28) Ammonium Sulfate (9.35) Comp. α-Alumina (12.75) — Sulfuric Acid (0.8) C 1:1:3 2.0 0.64 Ex. 12 θ-Alumina (2.56) Citric Acid (4.28) H₂O₂ (2.56) Ammonium Sulfate (9.35) Comp. α-Alumina (12.75) — Sulfuric Acid (0.8) C 1:1:3 2.0 0.73 Ex. 13 θ-Alumina (2.56) Citric Acid (4.28) H₂O₂ (2.56) Ammonium Sulfate (9.35) Comp. α-Alumina (12.75) A H₂O₂ (2.56) — 1:1:3 2.2 0.64 Ex. 14 θ-Alumina (2.56) Sulfuric Acid (0.8) Ammonium Sulfate (9.35) Citric Acid (4.28) Comp. α-Alumina (12.75) A H₂O₂ (2.56) — 1:1:3 2.2 0.64 Ex. 15 θ-Alumina (2.56) Sulfuric Acid (0.8) Citric Acid (4.28) Ammonium Sulfate (9.35) Comp. α-Alumina (12.75) — H₂O₂ (2.56) B 1:1:3 2.6 0.73 Ex. 16 θ-Alumina (2.56) Sulfuric Acid (0.8) Citric Acid (4.28) Ammonium Sulfate (9.35) Comp. α-Alumina (12.75) — H₂O₂ (2.56) B 1:1:3 2.6 0.73 Ex. 17 θ-Alumina (2.56) Ammonium Sulfate (9.35) Sulfuric Acid (0.8) Citric Acid (4.28) Comp. α-Alumina (12.75) — — — 1:—:4 2.7 0.55 Ex. 18 θ-Alumina (2.56) H₂O₂ (2.56) Sulfuric Acid (0.8) Citric Acid (4.28) Ammonium Sulfate (9.35) Inside the parenthesis ( ) shows formulation amounts (% by weight), and balance is water.

As shown in the results of Tables 4 and 5, it can be seen that the polishing rate after the storage at 60° C. of each of the polishing compositions obtained from the polishing composition kit of Examples 7 to 18 is maintained at a high level with excellent reproducibility as compared to the case of the polishing rate of Reference Example 3. By contrast, the polishing rate after the storage at 60° C. of each of the polishing compositions obtained from the polishing composition kit of Comparative Examples 12 to 18 is dramatically decreased as compared to the polishing rate of the case where the polishing composition was evaluated for the polishing property immediately after the preparation without storage (Reference Example 4).

In addition, each of the objects to be polished of the aluminum alloy substrate obtained in Examples 1 to 18 does not have surface defects such as scratches, and has excellent surface smoothness.

INDUSTRIAL APPLICABILITY

The polishing composition kit for a magnetic disk of the present invention may be suitably used for the manufacture of a high-quality magnetic disk substrate such as hard disks.

The present invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. 

1. A polishing kit for a magnetic disk comprising: (A) a slurry comprising an alumina; (B) an oxidizing agent solution comprising an oxidizing agent; and (C) an acid agent solution comprising an acid.
 2. The polishing kit according to claim 1, wherein the alumina is α-alumina and θ-alumina, wherein the oxidizing agent is hydrogen peroxide, and wherein the acid is citric acid and sulfuric acid.
 3. A polishing kit for a magnetic disk comprising: (A) a slurry comprising an alumina; and (D) an additive solution comprising an oxidizing agent and an inorganic acid.
 4. The polishing kit according to claim 3, wherein the alumina is α-alumina and θ-alumina, wherein the oxidizing agent is hydrogen peroxide, and wherein the inorganic acid is sulfuric acid.
 5. The polishing kit according to claim 3, further comprising an acid agent solution (c) comprising an organic acid.
 6. The polishing kit according to claim 5, wherein the organic acid is citric acid.
 7. A polishing kit for a magnetic disk comprising: (A) a slurry comprising an alumina; and (C) an acid agent solution comprising an acid, wherein the polishing kit is used with an oxidizing agent solution (B) comprising an oxidizing agent.
 8. The polishing kit according to claim 7, wherein the alumina is α-alumina and θ-alumina, wherein the acid is sulfuric acid, and wherein the oxidizing agent is hydrogen peroxide.
 9. A polishing process for a magnetic disk substrate, comprising the steps of: feeding a liquid mixture comprising (A) a slurry comprising an alumina, (B) an oxidizing agent solution comprising an oxidizing agent, and (C) an acid agent solution comprising an acid to a space between the magnetic disk substrate and a polishing cloth; and polishing the magnetic disk substrate with the liquid mixture.
 10. A polishing process for a magnetic disk substrate, comprising the steps of: feeding a liquid mixture comprising (A) a slurry comprising an alumina, and (D) an additive solution comprising an oxidizing agent and an inorganic acid to a space between the magnetic disk substrate and a polishing cloth; and polishing the magnetic disk substrate with the liquid mixture.
 11. The polishing process according to claim 10, wherein the liquid mixture further comprises (c) an acid agent solution comprising an organic acid.
 12. A method for manufacturing a polished magnetic disk substrate comprising the steps of: (1) mixing (A) a slurry comprising an alumina, (B) an oxidizing agent solution comprising an oxidizing agent, and (C) an acid agent solution comprising an acid to give a polishing composition; (2) pressing the magnetic disk substrate against a polishing cloth of a polishing platen while applying pressure; and (3) moving the magnetic disk substrate and the polishing platen while feeding the polishing composition prepared in step (1) to a space between the magnetic disk substrate and the polishing cloth, thereby polishing the magnetic disk substrate.
 13. A method for manufacturing a polished magnetic disk substrate comprising the steps of: (1) mixing (A) a slurry comprising an alumina, and (D) an additive solution comprising an oxidizing agent and an inorganic acid to give a polishing composition; (2) pressing the magnetic disk substrate against a polishing cloth of a polishing platen while applying pressure; and (3) moving the magnetic disk substrate and the polishing platen while feeding the polishing composition prepared in step (1) to a space between the magnetic disk substrate and the polishing cloth, thereby polishing the magnetic disk substrate.
 14. A method for manufacturing a polished magnetic disk substrate comprising the steps of: (1) mixing (A) a slurry comprising an alumina, (D) an additive solution comprising an oxidizing agent and an inorganic acid, and (c) an acid agent solution comprising an organic acid to give a polishing composition; (2) pressing the magnetic disk substrate against a polishing cloth of a polishing platen while applying pressure; and (3) moving the magnetic disk substrate and the polishing platen while feeding the polishing composition prepared in step (1) to a space between the magnetic disk substrate and the polishing cloth, thereby polishing the magnetic disk substrate. 